Former US senators Trent Lott and John Breaux have been hired to lobby for companies that want to preserve the option of reducing their corporate tax bills by moving their legal addresses overseas.

Nine US companies that have sought mergers for tax reasons, are considering doing so or are targets of such deals have been pressuring lawmakers since April in regard to legislation to stop the practice, federal disclosure reports show.

They include Medtronic, which is seeking to acquire Dublin-based Covidien. Medtronic paid Breaux-Lott Leadership Group $200,000 (€150,000) in June to try to block legislation from moving forward. Breaux, a Democrat, was once a member of the Senate Finance Committee. Lott, a Republican, is a former Senate majority leader.

US President Barack Obama has ordered officials to find ways to block the deals without congressional action.

House Speaker John Boehner, an Ohio Republican, wrote an opinion piece for Politico over the weekend, urging the president not to act unilaterally.

Democrats and Republicans have criticised companies moving out of the US, but Republicans see cutting tax rates at home as the solution while Democrats want to make it harder to move abroad.